I want to brew a one gallon batch of a few beers to determine if I want to invest the time and $ in a 5 gallon batch.

So here's what I'm thinking of doing.

1. Divide all ingrediants by 5
2. Put all grains in grain bag and place in large pot
3. Add adjusted amount of mash water to pot at specific temp
4. After one hour mash, remove bag, pour water through filter into brew pot
5. Place bag back in pot and add sparge water to reach required pre boil volume (i'm assuming around 1.5 gallons to achieve a 1 gallon post boil).
6. Let sparge water sit around 10 minutes. Remove grain bag, and add sparge water to brew kettle.
7. Brew as usual.

PS - do I use 1/5 the amount of yeast as well or do I use the whole packet?

You can just mash in your brewpot, that's the advantage of the bag, no need to filter. Make sure it's a big bag so you can stir the grains well and ensure they are all in contact with the water. With just a 1 gallon batch you should be able to do a full volume mash without sparge if you want. Alternatively you could dunk sparge in a second pot, though you don't really need to let it sit too long in the sparge water just open the bag and stir it up really well. That's how I do my 3 gal stovetop BIAB batches, the full mash usually won't quite fit in the old 5 gal pot I use for a boil kettle.

You can just mash in your brewpot, that's the advantage of the bag, no need to filter. Make sure it's a big bag so you can stir the grains well and ensure they are all in contact with the water. With just a 1 gallon batch you should be able to do a full volume mash without sparge if you want. Alternatively you could dunk sparge in a second pot, though you don't really need to let it sit too long in the sparge water just open the bag and stir it up really well. That's how I do my 3 gal stovetop BIAB batches, the full mash usually won't quite fit in the old 5 gal pot I use for a boil kettle.

So, it wouldnt be better to stick with the same mash water to grain ratio even with a 1 gallon batch?

It's up to you, lots of folks do full volume mash/no sparge with BIAB or even in a traditional tun. The main concern would be mash pH if you have extreme water. If you have the room though it makes it nice and simple.

It's up to you, lots of folks do full volume mash/no sparge with BIAB or even in a traditional tun. The main concern would be mash pH if you have extreme water. If you have the room though it makes it nice and simple.

Sounds good! How about the yeast? do I only use 1/5th OR the whole bag?

If you are using dry yeast, the calculators usually show 2 g of yeast which is ~1/5 of a package. I usually use 2.5 g to 3 g and get 4 batches out of a package.

Your method looks fine except that you will need to use more water, based on my experience, depending on your boil off rate, and depending on which method you use (no sparge BIAB vs traditional mash volumes with batch sparge, for example). I use between 1 3/4 and 2 gallons to get to 1 gallon. I haven't exactly figured it out since I don't know how much water the grain soaks up. I just know where the water level needs to be in the brew kettle prior to the boil.

If you are using dry yeast, the calculators usually show 2 g of yeast which is ~1/5 of a package. I usually use 2.5 g to 3 g and get 4 batches out of a package.

Your method looks fine except that you will need to use more water, based on my experience, depending on your boil off rate, and depending on which method you use (no sparge BIAB vs traditional mash volumes with batch sparge, for example). I use between 1 3/4 and 2 gallons to get to 1 gallon. I haven't exactly figured it out since I don't know how much water the grain soaks up. I just know where the water level needs to be in the brew kettle prior to the boil.

Thanks for the info. just want to go with small batches for time being unless its a beer i love. Why brew 5 gallons of a beer that is only so-so?